Project Summary Severe destructive behavior represents a comorbid condition of developmental disability for which risk increases with intellectual disability severity, communication deficits, and co-occurring autism spectrum disorder.24,78 Destructive behavior, such as self-injurious behavior and aggression, causes harm to the child and others and increases the risk for institutionalization, social isolation, physical restraint, medication over- use, service denial, and abuse.79 Clinicians have used functional analyses to identify the variables that reinforce or motivate destructive behavior and to develop effective, function-based treatments.4 Functional communication training (FCT) is an empirically supported, function-based treatment that decreases destructive behavior. The clinician teaches the child to use the functional communication response (FCR) to request the reinforcer for destructive behavior, and destructive behavior is on extinction during FCT.6,39 For example, if functional-analysis results showed that attention reinforced destructive behavior, the clinician would provide attention when the child used the FCR (?Play with me, please.?) and would not provide attention for destructive behavior. One limitation of FCT is that relapse, an increase in destructive behavior after initially effective treatment, often occurs when we transfer treatment to new therapists, caregivers, or settings or when change agents implement it incorrectly.8,39,80,81 Behavior analysts describe relapse as (a) renewal when the treatment context changes (e.g., transfer treatment from clinic to home),12 (b) resurgence when the FCR does not produce reinforcement,82 and superresurgence when renewal and resurgence co-occur and cause higher levels of relapse than that produced by either alone,14 and (c) reinstatement when the caregiver mistakenly provides reinforcement at unplanned times.83 Our research from Period 1 of this project, based on behavioral momentum theory, suggested that signaling when the FCR will and will not produce reinforcement during our multiple-schedule FCT (mult FCT) procedure: (a) prevented extinction bursts, (b) facilitated reinforcement- schedule thinning, and (c) prevented or mitigated relapse when caregivers did not deliver planned reinforcement for the FCR.9 In addition, our related preliminary research showed that mult FCT often: (a) rapidly reduced destructive behavior, (b) facilitated treatment transfer across contexts without evoking renewal, and (c) reduced the need for a punishment component. We will conduct a randomized clinical trial to compare the effectiveness of mult FCT to traditional FCT, which does not signal reinforcement availability and unavailability, for mitigating renewal, superresurgence, and reinstatement. We also will test whether mult FCT + stimulus fading, in which we conduct each context change in gradual steps, will further reduce treatment relapse. This novel project has the potential to change the way researchers and clinicians analyze and prevent treatment relapse, thereby markedly improving the long-term outcomes for children and families afflicted by these debilitating behavior disorders.